A three dimensional stacked semiconductor memory such as a 3D-NAND flash memory or the like includes a laminated film in which different types of layers are laminated alternately multiple times (see, e.g., Patent Document 1). The laminated film may have a deep recess (hole such as opening and/or trench such as groove) penetrating through a base film. Such a deep hole is formed by plasma etching.
In the plasma processing for etching such a multilayer film, when each of the different layers of the laminated film is etched, the number of etching is increased as the number of laminated layers is increased, which leads to decrease in throughput. To that end, the laminated film is plasma-etched by using a processing gas containing gases required for etching the respective different layers. As a result, a recess penetrating through the different layers can be formed by performing the plasma etching only once. In order to etch the laminated film, a mask layer having patterned openings for forming recesses in the laminated film is formed on the laminated film and, then, the laminated film is plasma-etched while using the mask layer as a mask.
Patent Document 1: Japanese Patent Application Publication No. 2009-266944
Meanwhile, the laminated film may include a layer (e.g., silicon nitride (SiN) layer) that is easily etched by the processing gas for etching the laminated film. A processing gas same as that used for the laminated film may be also used in the case of etching such multilayer film having the SiN layer. However, as the etching proceeds, from the SiN layer, through the laminated film, a side surface of the SiN layer exposed in the formed recess is also etched.
The side surface of the SiN is etched such that the opening width is gradually increased in a depth direction of the SiN layer. Therefore, an abnormal etching shape, e.g., bowing, occurs at the recess formed from the SiN layer through the laminated film.